In order to create satisfactory tactile and visual experiences for users, more and more smartphones use metal shells. In the related art, an integral phone-body-forming process, also known as unibody process, is used to forge a single piece of metal into a metal shell of a basic shape, and then a large amount of work is needed to forge and process the metal shell into a specific shape through computerized numerical control (CNC) machines. Typically, after being forged, the metal shell needs to include one or more plastic gripping structures, such that the metal shell can be fixed to the smartphone through the plastic gripping structures. As such, the required thickness of the metal material depends on the thickness of the plastic gripping structures. That is, the thickness of the metal material needs to be greater than the thickness of the plastic gripping structures, to ensure the metal shell can be fabricated from the metal material. For example, if a metal shell has a side wall of 0.9 mm thick and a plastic gripping structure of 1.5 mm thick, the thickness of the metal material used for fabricating the metal shell is required to be at least 2 mm such a great thickness prolongs the time for a CNC machine to processing and forging the metal material, and increases the difficulty of performing stamping operation on the metal material.